The present invention relates to digital analysis of the operation of devices, and more particularly to a digital video probe for retrieving digital data from a device under test and displaying the data in analog form.
With the increasing amount of digital video equipment being introduced into broadcasting systems, particularly into critical program paths as well as for "special effects" applications, it is important to have means for quickly identifying and repairing faulty equipment. However, although digital equipment is stable and reliable, the signal paths can be quite complex and the digital implementation of some functions, such as filtering, can appear more complicated than the analog equivalent. Also the multi-bit structure can make signal tracing more difficult. In a broadcast television studio it is important that any equipment failures be identified quickly and the offending equipment be repaired or replaced in a minimum amount of time to prevent a loss of air time. To do this a simple to use failure detection instrument is necessary since generally such first-line service will be performed by persons unfamiliar with the details of the equipment operation.
Typical analog troubleshooting involves signal tracing by observing the waveform at various points of a device under test on an oscilloscope. By testing at various points along a signal path the location of a fault can be isolated by observing where the signal deviates from the expected waveform. However in a digital system the signal waveform may not indicate the nature of the fault. It has been suggested by D. J. Bradshaw in "Fault Diagnosis in Digital Video Equipment", EBU Review - Technical No. 214, December 1985, that the digital signals be converted to an analog waveform by a digital to analog converter (DAC) and displayed using an oscilloscope or a picture monitor. Alternatively signature analysis has been proposed as a preferred technique to provide "signal tracing" fault analysis, but such a fault diagnosis technique would have to be designed into the circuit which would add to the expense of the digital equipment.
What is desired is a simple to use fault diagnosis instrument for use with digital equipment for providing initial fault diagnosis without the need for designing special circuitry into the digital equipment.